Lowly elastic polyimide is used as a material with low stress and thermal resistance in protective films for use in semiconductors, insulation films of multilayer circuit substrates, adhesive films of semiconductors, cover lays of flexible circuit substrates and the like (see patent documents 1, 2, 3, 4 and 5).
Because such polyimide with low elasticity is obtained by the copolymerization of silicone-containing diamine or tetracarboxylic anhydride, however, such polyimide has never been possibly used for applications involving the generation of serious disadvantages due to silicone contamination, such as HDD application and some semiconductor applications.
As described above, heat resistant resins with low elasticity, being usable with no generation of contamination in production apparatuses of HDD and semiconductors, have been desired.
Further, some cleaning substrates for the dusting of the inside of such apparatuses contain sheets comprising synthetic resins such as acrylic resin on silicone wafer (see patent documents 6 and 7), However, it cannot be said that the thermal resistance of such substrates at the pre-processing step demanding thermal resistance in particular is satisfactory. Therefore, a highly thermally resistant cleaning substrate has been desired.
Particularly, the dusting wafer in the first-half process of producing semiconductor apparatuses, particularly PVD apparatus is frequently used at high temperature. Therefore, various physical properties such as thermal resistance within a temperature range for the dust proofing of these apparatuses and stability are now demanded,    [Patent document 1] JP-A-5-170901    [Patent document 2] JP-A-6-73178    [Patent document 3] JP-A-6-207024    [Patent document 4] JP-A-6-73178    [Patent document 5] JP-A-2002-50854    [Patent document 6] JP-A-2001-351960    [Patent document 7] JP-A-2002-18377